1. Technical Field
Embodiments of the present invention are related to the fields of data processing and data communication, and in particular, to wireless networking.
2. Description of Related Art
An Institute of Electrical and Electronic Engineers (IEEE) 802.11e standard (approved 2005, IEEE Standards Board, Piscataway, N.Y.), among other things, define aspects of Worldwide Inoperability for Microwave Access (WiMAX) for Wireless Metropolitan Area Networks (MANs). Among the functionalities supported by WiMAX is high-speed seamless handoff (HO) of Mobile Subscriber Station (MSS) from one Base Station (BS) to another, that does not compromise subscriber or network security.
In order to support high-speed secure HO model, an automatic key-derivation for HO was defined in which an authentication key (AK) for target base stations (BS) is derived prior to HO by both the target BS and MSS while still connected to the source BS. Thus, MSS can HO without the need to perform lengthy authentication, authorization and accounting (AAA) session and skipping the major time-consuming phase of connecting to a new BS, leading to the low latency HO that is both seamless and secure.
Typically, the mechanism of deriving AK automatically from a parent key (Pairwise Master Key—PMK) creates a fresh context called AK Context for this derived AK at both the BS and MSS. A fresh AK context can be derived only once (per BS and PMK) and is used until the key (PMK) is expired in order to maintain security (If a fresh context will be created twice for the same AK—it is a security hole that allows reply attacks). Per WiMAX, the default implementation is to cache the AKs and AK Contexts till the corresponding PMK is no longer valid (i.e. expired) which can be several days in most networks. This can lead to BS's caching a large number of AKs and AK Contexts belonging not only to MSSs currently active in the network but also MSS that had joined and left the network but still have valid PMKs. Since PMKs can be cached for few days, the number PMKs, AKs and AK Contexts that can be cached is potentially quite large, leading to long searches and large memory requirements in BS leading to a costly BS.